The invention relates to electronic components, and it relates, more particularly to a chip inductor of the type having air-core coil that serves as an RF choke.
By comparison with the usual discrete wired inductors, chip inductors are physically smaller, can be manufactured at less expense, and are more suitable for use in automatic insertion machines for circuit boards. The conventional chip inductors are typically made utilizing a conventional layer technique and in part commonly formed as rectangular or cylindrical, wire-wound magnetic cores, in prticular ferrite cores.
To produce chip inductors utilizing this layer technique, a support is coated with a layer of magnetic material and on this layer a conductor track formed as a coil is applied. One conventional approach is to provide inductor sections that are combined with additional inductor sections in a stack, depending on the desired inductance. For the through-contacting of the ends of the individual coils or sectional inductors, numerous methods not explained in detail here are known and utilized by those skilled in this art.
These chip inductors are desirable due to their compact construction, capability of being soldered directly on printed circuit boards, and require no additional wires are connecting elements. A significant disadvantage, however, is their costly manufacture, due to the layering technique of manufacture. Layer thickness fluctuations of the magnetic layer, inevitable in the manufacture, cause undesirable fluctuations in the L and Q values of the inductors. As material for the coil conductor tracks, silver or a silverpalladium alloy must be used, for example, and a high ohmic resistance or the conductor tracks must be accepted. As the conductor tracks are embedded in the magnetic layer, magnetic saturation, caused by the small sized magnetic circuit occurs, even at low values. Therefore, the d-c premagnetization properties of the chip inductor are consequently reduced. Also, the number of coil turns is limited and hence the adjustable inductance is limited.
Another conventional chip inductor has a rectangular ferrite core with rectangular or cylindrical center portion as winding support and flanges formed on the support in one piece, which also has a rectangular cross-section. The contacting of the winding ends occurs by means of electrically conducting layers arranged at the flanges on the end faces, on which layers the winding ends are soldered. The finished winding is here embedded in synthetic resin and together with the flanges forms a block.
To eliminate the disadvantages of these conventional chip inductor components in terms of manufacture, partly of an electrical nature and partly of a mechanical nature, there has been proposed moreover a chip inductor equipped with a ferrite spool core. The wound spool core is embedded in a parallelepipedal seal, against the one end faces of which the ends of strip-shaped connecting elements apply, which by their other ends are contacted with electrically conducting solderable layers of the end faces of the spool core flanges (see German patent document No. 3,225,782 Al). A disadvantage of this design is that it takes two machining steps to attach the connecting elements to the coil core. First a metal plate much be glued onto the coil form, whereupon the actual connecting strip is soldered on.
In U.S. Pat. No. 3,585,553 a chip inductor is disclosed with a solid ferrite core portion of parallelepipedal form which comprises a winding space wound in one course and recessed relative to the parallel front ends of the core portion and in the region of these front ends, has cutouts for bringing out the winding ends. The recesses extend in lengthwise direction of the chip inductor, and the surfaces of the front ends on either side thereof are covered with electrically conducting layers, over which the contacting of the winding ends occurs.
While this chip inductor is of relatively simple design, the electrically conducting contact layers require a relatively complicated process in manufacturing which increases their cost.
It is an object of the present invention to provide an electronic component of the foregoing mentioned kind which can be produced at low cost and is particularly suitable for the manfacture of chip inductors.
Another object of the invention is to provide a chip inductor which meets the requirement of certain electronic equipments also with respect to high resonance frequencies insofar as it can be wound e.g. in a single course and, despite small dimensions, with a high number of turns.
A further object of the invention is to provide a chip inductor wherein the connecting elements of this electronic component are to be constituted so that they satisfy both the high mechanical requirements e.g. in assembly and also the mechanical stresses caused the possible occurrence of deflections experienced by circuit boards.